Method of seasoning wood



Patented June 10, 1930 PATENT OFFICE 'ronmis'r srnnA ron SHINN, or Ari-roan, ILLINOIS METHOD or SEASONING WOOD.

No Drawing.

The present invention relates to methods of seasoning material such as wood in the form of posts, poles, piles, railroad ties, lumber, etc.

The general object of the invention is to provide a new and improved method particularly adapted for the rapid seasoning of Wood or other material whichis afterward to be impregnated with some preservative. By seasoning I mean removing part of the mois- 1o 'ture present in the wood prior to the seasoning treatment, or otherwise making the Wood less resistant to the absorption of preservative. The method is particularly intended for use in the seasoning of green wood, that is,

wood which has been recently cut, but it is not limited to that use. Fresh cut or green wood contains in its pores a large amount of moisture which renders dificult the impregnation of the wood with a preservative; and

L my method hereinafter described, permits the rapid removal of a large proportion of such moisture from the wood, and leaves the wood in a condition to be readily impregnated with a preservative in any suitable and wellknown manner.

The present invention is characterized by the facts that the wood to be seasoned is subjected to a vacuum treatment preceded by steam and compressed air treatments. Preferably, the steam treatment precedes the compressed air treatment; but the order of these treatments may be reversed Without departing from the scope of my invention.

The method of seasoning wood which comprises my invention may be carried out with a retort, preferably of the horizontal cylindrical type, usually found in wood treating plants. In connection with the retort there should be provided means such as a steam boiler for supplying steam to the retort; means such as a condenser and a vacuum pump for exhausting the retort to a pressure approaching a vacuum, say 28.5 or 29 inches of mercury in a manometer; and an air-compressor by which compressed air may be furnished to the retort to raise the pressure in the latter considerably above atmospheric pressure, say to lbs. per square inch. The arrangement of piping connecting the boiler,

compressor to the retort, and the arrangethe condenser and vacuum pump, and the air- Application filed October 15, 1927. Serial No. 226,519.

ment of control valves in such piping will be obvious to one skilled in the art. 7

With such apparatus as that above mentioned, my improved method of seasoning wood may be successfully carried out in the following manner upon Wood arranged in the usual way in a closed retort:

(a) .The wood to be treated is first heated by subjecting it to a bath of steam at a pressure considerably above atmospheric pressure, which heats the wood and its Water content to a temperature considerably higher than 212 Fahrenheit, but not high enough to in any manner injure the wood. A steam pressure of 20 lbs. per square inch maintained in the retort for a period of one hourhas been found to be satisfactory. During this steam treatment any water condensed from the steam is preferably drained from the retort so as not to permit its reaching the timbers.

(b) At the end of the steaming period, the supply of steam is cut oft and the pressure in the retort is increased by forcing air into the retort by means ofan air compressor. The wood to be treated in the retort is held under such air pressurefor a length of time sufficient, in the opinion of the operator, to make sure that the compressed air in the retort has worked thoroughly into the cells of the wood to be treated. For example, an air pressure of 80 lbs. per square inch maintained for one hour is generally suificient. The air compressor is then cut off from the retort and the pressure within the latter is allowed to quickly exhaust to atmospheric pressure which results in the expulsion of some water from the wood due to the action of the air at high pressure in escaping from the pores of the latter. This water should be drained from the retort. I

(0) The retort containing the wood to be seasoned is then subjectedto a high vacuum, say 28.5 or 29. inches of mercury in a ma nom'eter, through the medium of a condenser and vacuum pump connected'to the retort. This vacuum treatment has the eflect of cans ing more of the water content of the Wood to come out of thelatter in the form of water vapor which is drawn out of the retort through the condenser and vacuum pump. In my Opinion this result is due both to the fact that the boiling point of water at this reduced pressure in the retort is far below the temperature to which the wood has been heated by the previous steam treatment, and to the escaping from the pores of'the wood of air either normally existing therein or forced into said pores during the previous compressed air treatment. This vacuum treatment is preferably continuned until water vapor ceases to come from the retort, this condition being apparent from observations of the well of the condenser.

As hereinbefore mentioned, the steam treatment (a) above described, instead of preceding may follow the compressed air treatment (12) also above described, and this modification is to be regarded as within the scope of my invention.

Ordinarily at the conclusion of the steam and compressed air treatments followed by a vacuum treatment as above mentioned, the wood has been seasoned sufiiciently to permit its proper impregnation by any suitable impregnating fluid, but if further seasoning or impregnating is desirable, the wood may again be subjected to these treatments.

When my method of seasoning is to be followed by the so-called full cell process of impregnating wood with a preservative, it will be found convenient to admit the preservative to the retort at the end of the vacuum treatment above described, without breaking the pressure within the retort may be restored to atmospheric pressure before the wood is treated with preservative.

After having been subjected to the method of seasoning above described, wood that was green before such treatment is actually capable of absorbing a preservative material to an extent by volume which compares favorably with the absorption which is obtained in the case of wood which has been air-seasoned in the usual manner. I believe that such result is due to the fact that the vacuum treatment is preceded by steam and compressed air treatments which seem to have the effect of increasing the exuding of moisture from the wood under the influence of the vacuum treatment.

WVhat I claim is:

1. A method of seasoning wood character ized by the facts that the wood is first subjected to a steam treatment, is then subjected to a compressed air treatment, and is then subjected to a vacuum treatment, such seasoning treatment being without the addition of preservative liquid.

2. A method of seasoning wood characterized by the facts that the wood is first heated by treatment with steam at a pressure considerably higher than atmospheric pressure, is then subjected to treatment by compressed air at a pressure considerably higher than the steam pressure, and is then subjected to a vacuum treatment, such seasoning treatment being without the addition of preservative liquid.

3. A method of seasoning wood characterized by the facts that the Wood is subjected to a vacuum treatment preceded by a treatment with steam at a pressure considerably higher than atmospheric pressure, and a treatment with compressed air at a pressure considerably higher than the steam pressure, such seasoning treatment being without the addition of preservative liquid.

4. A method of seasoning wood characterized by the facts that the wood is subjected to separate treatments Withsteam alone and compressed air alone and is then subjected to a treatment at a pressure far below atmospheric pressure.

In testimony whereof, I have afiixed my signature to this specification.

FORREST STREATOR SHINN. 

